It is known that a device comprising a certain positively charged lipid (for example, a cationic liposome) is useful for the transfer of genes into the cell (e.g. JP-A-4108391, WO91/17424). It is also known that when a nucleic acid such as a double-stranded RNA is administered together with a device such as a cationic liposome, a potentiated interferon inducer action is realized (U.S. Pat. No. 5,049,386). It is generally conjectured that since the nucleic acid of, for example, a gene is negatively charged, it forms a complex with a cationic liposome and the complex becomes fused to the cell membrane and the nucleic acid of the gene or the like finds its way into the cell.
As said cationic liposome, Lipofectin (trademark, Bethesda Research Laboratories Life Technologies Inc.) comprising N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride (hereinafter referred to as DOTMA) and dioleoylphosphatidylethanolamine in a ratio of 1:1 is well known.
However, because DOTMA as a component of Lipofectin is a quaternary ammonium compound and, therefore, has high hemolytic toxicity, it is not suitable for pharmaceutical use.
An attempt has been made to enhance the effect of the liposome by replacing the DOTMA of Lipofectin with a cholesterol derivative (Third International Symposium on Catalytic RNAs and Targeted Gene Therapy for the Treatment of HIV Infection, Dec. 6-11, 1992).